The separation of aromatics from hydrocarbon feed streams comprising mixtures of aromatics and non-aromatics by solvent extraction is a process which has long been practiced in the refining industry especially in the production of lubricating oil. The process involves the use of solvents such as phenol, furfural, n-methyl pyrrolidone which are selective for the aromatic components present in the hydrocarbon feed streams. These solvents typically are combined with water to provide a solvent mixture containing up to about 10 vol. % water. The hydrocarbon stream and the selective solvent or solvent mixture are combined, typically and preferably under counter-current conditions. The contacting results in concentration of the aromatic component in the selective solvent. Because the solvent and the hydrocarbon oil are of different densities and generally immiscible, after the contacting the aromatics rich solvent phase separates from the mixture thereby resulting in an aromatics rich solvent phase called the extract and an aromatics lean non-aromatics rich product phase called the raffinate. Because no solvent extraction process can be one hundred percent selective, the aromatics rich extract phase contains a minor but economically significant quantity of non-aromatic hydrocarbon which constitute good lube oil molecules.
Various processes have been proposed for recovering these good lube oil molecules present in the extract phase. Some of these do not provide for maximum recovery of the desired molecules. Others require increased capital costs or result in increased operating expenses. Thus, there remains a need for improvements in recovering lube oil molecules from a solvent extract which will provide greater yields at lower investment and operating costs.